Conventionally, a glow plug used for ignition assist or the like of a diesel engine includes a cylindrical housing having an axial hole extending in the axial line direction, a heater inserted through the axial hole, and the like. Further, there is a case that a ceramic heater is employed as the heater. An existing ceramic heater has a configuration in which a conductive ceramic heating element is arranged inside an insulating ceramic base member and at least an outer surface of the heater is formed of ceramic.
Further, in recent years, a glow plug with a pressure sensor provided with a function for sensing the pressure of a combustion pressure or the like has been proposed as a glow plug. In such a glow plug with the pressure sensor, the ceramic heater is mounted in a state of being relatively displaceable with respect to a housing, and a front end part of the ceramic heater protrudes from the front end of the housing. When the ceramic heater receives the combustion pressure and the like and is relatively displaced, such relative displacement is transferred to the pressure sensor via a metallic transmission member connected to the ceramic heater, and a signal corresponding to the amount of the relative displacement of the ceramic heater (that is, the pressure applied to the ceramic heater) is outputted from the pressure sensor (for example, see JP-A-2011-144978).
In addition, in order to allow the ceramic heater to be relatively displaceable with respect to the housing, the ceramic heater is mounted to the housing via a cylindrical metallic movable member that is deformable in an extendible and contractive manner along the axial line direction. Here, when one whose outer surface is formed of ceramic is used as the ceramic heater, the outer surface of the ceramic heater cannot be directly welded to the movable member by laser welding or the like. Thus, in some cases, after the ceramic heater is arranged on the inner circumference of a cylindrical metallic outer cylinder and the ceramic heater is fixed to the outer cylinder by press-fit or the like, the movable member is welded to the outer circumference of the outer cylinder by laser welding or the like, so that the ceramic heater is indirectly connected to the movable member. In other words, the ceramic heater is connected to the movable member via the outer cylinder in some cases.
Further, similarly to the movable member, the transmission member cannot be directly welded to the outer surface of the ceramic heater. Thus, in some cases, after the ceramic heater is arranged on the inner circumference of a cylindrical metallic ring member and the ceramic heater is fixed to the ring member by press-fit or the like, the transmission member is welded to the outer circumference of the ring member by laser welding or the like, so that the ceramic heater is indirectly connected to the transmission member.